Environmental regulation of flowering time in heliotrope (Heliotropium arborescens L. cv. Marine)

The aim of this study was to examine the environmental regulation of flower initiation and subsequent development in heliotrope (Heliotropium aboresce ns L. cv. Marine). Five experiments were conducted, two examined whether fl owering could be advanced by cool temperatures. The duration of cool temper ature required to induce rapid flowering was also investigated. The final t hree experiments examined the effects of light integral, photoperiod and te mperature on flower initiation and development. It was found that plants grown for 9 days at 10 degrees C and than transfer red to 20 degrees C flowered significantly earlier (first flowering recorde d after 55 days) than plants held constantly at 20 degrees C (65.9 days to flowering). Plants grown at a constant temperature of 20 degrees C had sign ificantly more leaves than all other treatments. This suggested that 'cool' temperatures, prior to initiation, advanced flowering. In a transfer exper iment, plants were moved from 10 to 20 degrees C at 3 days intervals post-p inching. Earliest flowering (by 20 days compared to the 20 degrees C consta nt treatment) occurred when plants were exposed to 10 degrees C for 9 days and then transferred to 20 degrees C. Photoperiod was shown to have no effect on either flower bud initiation or development (postinitiation). Both temperature and light integral strongly influenced flower development post-flower bud initiation. However, the resp onse to temperature plotted in terms of the reciprocal of days to flowering was non-linear. (C) 2000 Elsevier Science B.V. All rights reserved.